Wrong locations of global import statements

You may have written code where global import statements are done within a Jython function.
As of Jython 2.5, this is not allowed anymore (in fact, it was not allowed in Python 2.1 but Jython 2.1 inadvertently allowed for it).

When executing the code against Jython 2.5, you will get messages such as:

SyntaxWarning: import * only allowed at module level

To fix your code, you have two options:

Move the global import statement out of the function and to the top of your script.

Numeric types

In Jython 2.1 numeric types were Py objects like PyInteger or PyFloat and as such had methods like toString(). In Jython 2.5 numeric types are more like native types and do not have these basic Object methods available. The difference was discovered when passing an integer into a jython function and then printing this value using the toString() method. In Jython 2.5 this results in the following error:

Some other Java methods can no longer be applied to numbers (which may require changing some client code). In general, when using Jython we should just use Jython functionality if available to avoid this type of problems.
The following example shows what happens when you try to move from "long" to "double" using java.lang.Number methods (to make a floating point division for example).